US 2012/0173031 A1 discloses a real time power point calibration system. To determine, as disclosed in its abstract, operating points of a photovoltaic array, an amount of power supplied by an alternate power source is adjusted. Thereto, as shown in FIG. 3 and as discussed in paragraph 0084, an indication of a current or a voltage at the photovoltaic array is used to determine whether an output of the photovoltaic array has reached a target current or voltage.